On April 5, the first data of the new observation cycle of the LIGO-Başak-KAGRA collaboration, which started a year ago, were published. The first reliably confirmed event was the GW230529 gravitational wave signal. This incident turned out to be unique and the second of its kind in the history of detectors. It turns out that one of the objects of gravitational interaction is the so-called mass gap between neutron stars and light black holes, and this is a new mystery.

According to data from the LIGO gravitational wave detectors, event GW230529 is the interaction of two objects; one has a mass of 1.2-2.0 solar masses, and the second has a mass more than twice as large (with 2.5-4.5 solar masses). The first compact object was identified as a neutron star, while the second fell into a mass range where nothing should be. Scientists have found faint black holes above the void, but not below it. Additionally, neutron stars cannot fall into this range. The assumption remains that scientists have discovered the lightest black hole, which has become a challenge for modern astrophysics.

A similar object of intermediate mass had already been observed in one of the previous observations by the LIGO-Virgo detectors; this was the signal of GW190814. But then in 2019 a signal was received about an object in the lower range of the mass range, which led us to suspect that it was the heaviest neutron star. The GW230529 signal has revealed a new mystery, but the gravitational wave observatory alone won’t be able to solve it. This requires observations at other intervals.

Meanwhile, GW230529’s signal was detected only by the LIGO observatory. Virgo Observatory in Italy and KAGRA in Japan were not able to see the data, so it is difficult to determine the direction of the event. At the same time, detecting the signal in a detector was a test of the new software that successfully filtered out the noise and isolated a useful and unique signal.

In January, the observatory was closed for planned maintenance and modernization. An observatory in Japan experienced an earthquake and had to be repaired. The new observing session will begin on April 10 and last until February 2025. In the first cycle, 81 events were recorded and data for the first of these, GW230529, was published. Overall, more than 200 gravitational wave events are expected to be recorded after the end of the cycle.